I know the Olympus 75mm f/1.8 is the best portrait prime in M43, and possibly in all mirrorless systems if not all systems. And, I do not own it because it is very expensive. The Sigma 60mm f/2.8 is shorter and slower, but much cheaper.

Here are Lenstip's resolution test results. Obviously the Olympus 75mm is much sharper at f/1.8 and f/2, but from f/2.8 we have an embarrassing revelation.

Olympus 75mm f/1.8

Sigma 60mm f/2.8

Sure the 75mm is a lot of lens, much faster, nicely built, .... .... but which one is sharper?